The OBD II system readiness tests (SRT) are:
- Heated oxygen sensor (HO2S) monitor
- Catalyst efficiency monitor
- Misfire detection monitor
- Fuel system monitor
- Comprehensive component monitor
- Evaporative emission system monitor
OBD II regulations require monitoring of the upstream heated oxygen sensor (HO2S) to detect if the deterioration of the sensor has exceeded emission thresholds. An additional HO2S is located downstream of the warm up- three way catalytic converter (WU-TWC), or after the pre-catalytic converter to determine the efficiency of the catalyst. Although the downstream HO2S is similar to the type used for fuel control, it functions differently. The downstream HO2S is monitored to determine if a voltage is generated. That voltage is compared to a calibrated acceptable range.
Catalyst Efficiency Monitor
The catalyst efficiency monitor is a self-test strategy within the powertrain control module (PCM) that uses the downstream heated oxygen sensor (HO2S) to determine when a catalyst has fallen below the minimum level of effectiveness in its ability to control exhaust emissions.
Misfire Detection Monitor
Misfire is defined as the lack of proper combustion in the cylinder due to the absence of spark, poor fuel metering, or poor compression. Any combustion that does not occur within the cylinder(s) at the proper time is also a misfire. The misfire detection monitor detects fuel, ignition or mechanically induced misfires. The intent is to protect the catalyst from permanent damage and to alert the customer of an emission failure or an inspection maintenance failure by illuminating the malfunction indicator lamp (MIL). When a misfire is detected, special software called ‘‘freeze frame’’ data is enabled. The freeze frame data captures the operational state of the vehicle when a fault is detected from misfire detection monitor strategy.
Fuel System Monitor
The fuel system monitor is a self-test strategy within the powertrain control module (PCM) that monitors the adaptive fuel table. The fuel control system uses the adaptive fuel table to compensate for normal variability of the fuel system components caused by wear or aging. During normal vehicle operation, if the fuel system appears ‘‘biased’’ lean or rich, the adaptive fuel table will shift the fuel delivery calculations to remove the bias.
Comprehensive Component Monitor
The comprehensive component monitor is a self-test strategy within the powertrain control module (PCM) that detects faults of any electronic powertrain component or system that provides input to the PCM and is not exclusively an input to any other OBD II monitor.
Evaporative Emission System Monitor
The evaporative emission (EVAP) system monitor is a self-test strategy within the powertrain control module (PCM) that tests the integrity of the EVAP system. When a fault occurs, the EVAP system monitor is reset to ‘‘NO’’ and a diagnostic trouble code (DTC) is set in the PCM memory. After the DTC is repaired the vehicle drive cycle must be driven to reset the monitor in preparation for Inspection Maintenance (I/M) testing.